er minor
improvements by the makers the admiralty compass, the card of which is
shown in figs. 1 and 2, was adopted by the government. Until 1876,
when Sir William Thomson introduced his patent compass, this compass
was not only the regulation compass of the British navy, but was
largely used in other countries in the same or a modified form. The
introduction of powerful engines causing serious vibration to compass
cards of the admiralty type, coupled with the prevailing desire for
larger cards, the deviation of which could also be more conveniently
compensated, led to the gradual introduction of the Thomson compass.
Several important points were gained in the latter: the quadrantal
deviation could be finally corrected for all latitudes; frictional
error at the cap and pivot was reduced to a minimum, the average
weight of the card being 200 grains; the long free vibrational period
of the card was found to be favourable to its steadiness when the
vessel was rolling. The first liquid compass used in England was
invented by Francis Crow, of Faversham, in 1813. It is said that the
idea of a liquid compass was suggested to Crow by the experience of
the captain of a coasting vessel whose compass card was oscillating
wildly until a sea broke on board filling the compass bowl, when the
card became steady. Subsequent improvements were made by E. J. Dent,
and especially by E. S. Ritchie, of Boston, Massachusetts. In 1888 the
form of liquid compass (fig. 5) now solely used in torpedo boats and
torpedo boat destroyers was introduced. It has also proved to be the
most trustworthy compass under the shock of heavy gun fire at present
available. The deflector is an instrument designed to enable an
observer to reduce the deviations of the compass to an amount not
exceeding 2 deg. during fogs, or at any time when bearings of distant
objects are not available. It is certain that if the directive forces
on the north, east, south and west points of a compass are equal,
there can be no deviation. With the deflector any inequality in the
directive force can be detected, and hence the power of equalizing the
forces by the usual soft iron and magnet correctors. Several kinds of
deflector have been invented, that of Lord Kelvin (Sir William
Thomson) being the simplest, but Dr Waghorn's is also very effective.
The use of the deflector is generally confined to experts.

_The M